1. Field of the Invention
The present invention relates to a centrifugal clutch and more particularly to a clutch lever for a centrifugal clutch used to apply axial pressure on one or more clutch disc assemblies as a function of the rotational speed of the engine; the clutch levers being formed with two pieces including a replaceable contact surface which obviates the need to replace the entire clutch lever when a clutch lever becomes damaged.
2. Description of the Prior Art
Clutch assemblies are used to couple the rotary power of the engine to the drive train of a vehicle. In automotive applications, the clutch is used to mechanically couple the flywheel, attached to the engine crank shaft, to the vehicle drive shaft by way of a clutch assembly. The flywheel enables torque from the engine to be transferred to the drive shaft. Known clutch assemblies are known to include a pressure plate and at least one clutch disk.
Various types of automotive clutch assemblies are known. In particular, both friction and centrifugal automotive clutch assemblies are known. Friction type clutch assemblies include a pressure plate and at least one clutch disc, disposed in a housing. An example of a friction type clutch assembly is described in detail in U.S. Pat. No. 7,082,661, hereby incorporated by reference. In general, in such friction type clutch assemblies, the pressure plate is mechanically coupled to the drive shaft and is mounted for axial movement from an engaged position to a non-engaged position. The clutch disc is splined so as to rotate with the drive shaft. In an engaged position, the pressure plate applies axial forces on the clutch disc against the flywheel to mechanically couple the clutch disc to the flywheel by friction in order to transmit the engine torque from the crank shaft to the drive shaft. In a disengaged position, the clutch disc does not contact the flywheel and therefore does not transmit the engine torque to the drive shaft. With such friction clutches, a manually operated clutch pedal inside the vehicle is used to engage and disengage the clutch.
Centrifugal clutches for automobiles are also known in the art. An example of a centrifugal clutch is disclosed in U.S. Pat. No. 4,485,905, hereby incorporated by reference. Such centrifugal clutches rely on centrifugal force to engage a clutch at high engine RPM and disengage the clutch at a relatively lower RPM. Such centrifugal clutches include a pressure plate and one or more clutch disc assemblies The pressure plate is attached to a vehicle flywheel, so as to rotate with the flywheel.
One or more clutch disc assemblies are splined to a common axis with respect to the drive shaft so that the drive shaft and the clutch disc rotate together. The clutch disc assemblies are configured for axial movement between the pressure plate and the flywheel. In an unengaged position, the clutch disc assemblies are spaced away from the flywheel. In such a position no rotational torque is transferred from the flywheel to the drive shaft. In an engaged position, the clutch disc assemblies make frictional contact with the flywheel causing the clutch disc assemblies and thus the drive shaft to rotate with the flywheel.
Such centrifugal clutch include a plurality of levers that are radially disposed and pivotably mounted with respect to the pressure plate. Weights are disposed on one or more of the clutch levers. In such centrifugal clutches, the pressure plate is directly mounted to the flywheel and thus rotates with the flywheel. Since the flywheel is directly connected to the engine crankshaft, the pressure plate rotates at the RPM (revolutions per minute) of the engine.
The clutch levers are used to apply a clamping force between the pressure plate and the flywheel to mechanically couple the clutch disc assemblies and thus the drive shaft to the flywheel. The clutch levers are pivotally connected to the pressure plate. Rotation of the pressure plate causes the clutch levers to pivot as a result of centrifugal force and exert a clamping force on the clutch disc assemblies. In particular, the levers are configured so that one end of the clutch levers exerts an axial force on the clutch disc assemblies in response to the centrifugal force to force the clutch disc assemblies to move axially toward the flywheel and make frictional contact with the flywheel. When a sufficient axial force is exerted on the clutch disc assemblies, the clutch disc assemblies make sufficient frictional contact with the flywheel to mechanically couple the clutch disc assemblies to the flywheel without slippage. Since the clutch disc assemblies are splined to the drive shaft, once the clutch disc assemblies are mechanically coupled to the flywheel, the rotating torque of the flywheel is transferred to the drive shaft. At low RPM, the clutch disc assemblies are spring biased in a direction away from the flywheel. Thus, at lower RPMs, the spring biasing force dominates and biases the clutch disc assemblies away from flywheel.
The clutch levers are known to undergo significant shear stress when the clutch levers are in the process of mechanically coupling the clutch disc assemblies to the flywheel. In time, the shear stress causes metal fatigue, resulting in one or more of the clutch levers breaking; normally somewhere between the point where the lever makes contact with the clutch disc and the pivot point of the lever. Due to the relatively high shear stress In racing applications, the levers may break after a few races. Such levers are precision parts and are thus relatively expensive. Any time a lever experiences a break, not only is the broken lever replaced but because of the metal fatigue problem discussed above, all levers are replaced. A typical lever for use in a racing application typically costs about $75-$110 for a lock-up lever and $170-$300 for a primary lever. In known applications, there can be eighteen (18) or more levers per clutch. This can cost, for example, about $2000-$3000 to replace all of the levers.
Thus, there is a need to come up with a better way to address the problem of replacement of the clutch levers used in conjunction with centrifugal clutches.